This application is based on Application No. 2002-58606, filed in Japan on Mar. 5, 2002, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to a control apparatus for a motor-driven power steering system of a motor vehicle (hereinafter also referred to simply as the motor-driven power steering control apparatus) which is adapted to generate a motor current required for generation of a steering assist torque on the basis of steering angular information and a steering torque in the power steering. More particularly, the present invention is concerned with a motor-driven power steering control apparatus which is capable of detecting abnormality of a steering angular information detecting means with high accuracy to thereby ensure enhanced reliability for the control of an electric motor employed in the power steering system.
2. Description of Prior Art
For better understanding of the concept underlying the present invention, description will first be made of a hitherto known or conventional motor-driven power steering control apparatus. FIG. 12 is a block diagram showing schematically, by way of example, a general arrangement of a conventional motor-driven power steering control apparatus which is disclosed in Japanese Patent Application Laid-Open Publication No. 2173/1992 (JP-A-4-2173).
Referring to FIG. 12, a controller 10 designed for controlling an electric motor 7 is supplied with an electric power from an vehicle-on-board battery 1 directly or by way of an ignition switch 2.
A steering mechanism 3 which is interlocked with a handle of a motor vehicle (not shown) includes a steering wheel implemented integrally with the handle for steering the motor vehicle with a steering torque Ts applied to the steering wheel.
The steering mechanism 3 is provided with a torque sensor 4 for outputting a detection signal indicating the steering torque Ts applied upon steering by a driver or operator as well as a steering angle sensor 5 for outputting a detection signal indicative of a steering angle xcex8s.
On the other hand, the motor vehicle is equipped with a vehicle speed sensor 6 for generating a detection signal indicative of a vehicle speed Vo.
The detection signals derived from the outputs of the various sensors 4 to 6 mentioned above (i.e., the signals indicative of the vehicle speed Vo, the steering angle xcex8s of the steering mechanism 3 and the steering torque Ts, respectively) are inputted to the controller 10 which responds thereto by supplying to the electric motor 7 a motor current im generated on the basis of the steering angle xcex8s as well as magnitude and direction of the steering torque Ts to thereby drive the electric motor 7.
The electric motor 7 is operatively or mechanically coupled to the steering mechanism 3 and generates a steering assist torque Ta applied to the steering wheel in accordance with the motor current im supplied from the controller 10.
To this end, the controller 10 includes a power supply circuit 11, an interface 12, a control unit generally denoted by 13, a motor drive circuit 18, a motor current detecting means 19, a relay driving circuit 20 and a fail relay 21.
The power supply circuit 11 is connected to the vehicle-onboard battery 1 by way of the ignition switch 2 and designed to supply an electric power to the control unit 13 when the ignition switch 2 is closed (i.e., turned on).
For performing control of the electric motor 7, the control unit 13 includes a steering assist torque control means 14, a steering angle detecting means 15, a steering velocity detecting means 16 and an abnormality decision means 17.
The motor drive circuit 18 supplies the motor current im to the electric motor 7 under the control of the control unit 13.
On the other hand, the motor current detecting means 19 is designed to detect the motor current im being supplied to the electric motor 7.
The relay driving circuit 20 is designed to drive or actuate the fail relay 21 when occurrence of abnormality is detected or decided by the control unit 13.
The fail relay 21 is supplied with electric power from the battery 1 to thereby stop operation of the motor drive circuit 18 in response to the relay driving circuit 20.
The steering angle detecting means 15 incorporated in the control unit 13 is designed to detect the steering angle xcex8s of the steering mechanism 3 on the basis of the detection signal derived from the output of the steering angle sensor 5. The steering angle xcex8s is then inputted to the steering assist torque control means 14, the steering velocity detecting means 16 and the abnormality decision means 17 as the steering angular information.
Further, the steering velocity detecting means 16 is designed to detect a steering angular velocity Vs on the basis of the rate of change of the steering angle xcex8s as a function of time to thereby input a steering angular velocity Vs as the steering angular information to the steering assist torque control means 14 and the abnormality decision means 17.
When the steering angle signal xcex8s or the steering velocity signal Vs indicates an abnormal value (when the steering angle xcex8s or the steering angular velocity Vs exceeds a maximum permissible value xcex8max or Vmax), the abnormality decision means 17 supplies to the steering assist torque control means 14 an abnormality decision signal indicating that the steering angle detecting means 15 including the steering angle sensor 5 or the steering velocity detecting means 16 suffers failure or abnormality.
At this juncture, it is to be added that in the system arrangement shown in FIG. 12, the steering angle xcex8s and the steering angular velocity Vs are detected as the steering angular information of the steering mechanism 3 while the motor current im is detected as rotational information of the electric motor 7.
The abnormality decision means 17 incorporated in the control unit 13 compares the steering angle xcex8s and the steering angular velocity Vs with the maximum permissible values xcex8max and Vmax, respectively, which conform with the vehicle speed Vo. When the steering angle xcex8s exceeds the maximum permissible value xcex8max or alternatively when the steering angular velocity Vs exceeds the maximum permissible value Vmax, the abnormality decision means 17 decides that the steering angle detecting means 15 or the steering velocity detecting means 16 is in a failure state (i.e., the state suffering abnormality).
Further, the abnormality decision means 17 is so designed as to decide as an abnormal state such situation where the steering angle xcex8s remains unchanged notwithstanding the change of the steering torque Ts brought about by the steering operation.
As is apparent from the foregoing, in the conventional motor-driven power steering system described above, parameters such as the vehicle speed Vo and the steering torque Ts which do not directly reflect the actual rotational operation of the steering mechanism 3 are adopted in the conditions for making decision as to occurrence of abnormality in the steering angle detecting means 15 and the steering velocity detecting means 16. Consequently, great difficulty is encountered in setting the conditions for the abnormality decision, giving rise to a problem that abnormality decision can not be made with high accuracy and reliability.
In the light of the state of the art described above, it is an object of the present invention to provide a motor-driven power steering control apparatus which is capable of making decision as to abnormality with ease and high accuracy upon occurrence of abnormality in the steering angle detecting means or the steering velocity detecting means by resorting to the use of only the parameters which directly reflect the actual rotational operation of the steering mechanism without making use of the vehicle speed and the steering torque in the abnormality decision conditions.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention a control apparatus for a motor-driven power steering system of a motor vehicle, which apparatus includes a steering mechanism operatively coupled to wheels of the motor vehicle for steering it in response to a steering torque transmitted from a steering wheel, a steering angular information detecting means for detecting steering angular information of the steering mechanism, a torque detecting means for detecting the steering torque of the steering mechanism, a controller for controlling a motor current on the basis of the steering angular information and magnitude and direction of the steering torque, an electric motor mechanically coupled to the steering mechanism for generating a steering assist torque corresponding to the motor current, the steering assist torque being applied to the steering wheel, a motor-rotational information detecting means for detecting rotational information of the electric motor, and an abnormality decision means designed to make decision that the steering angular information detecting means is abnormal when a difference between the steering angular information and the rotational information is not smaller than a reference value preset for comparison.
With the arrangement of the motor-driven power steering control apparatus described above, it is possible to make decision as to abnormality of the steering angular information detecting means with high accuracy and reliability by making use of only the parameters which reflect directly the actual rotational operation of the steering mechanism without involving substantially any appreciable complexity in the system configuration.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments there of taken, only by way of example, in conjunction with the accompanying drawings.